The present invention relates to a total electric type or a total hydraulic type steering apparatus in which a steering wheel of a vehicle and a steered tire wheel are not mechanically connected. More particularly, the present invention relates to a steering wheel position compensating apparatus which compensates a deviation in a positional relation between a steering wheel position (a steering wheel angle) and a wheel angle of the steered tire wheel.
Conventionally, there is a structure in which a total hydraulic type steering apparatus is equipped, in an industrial vehicle, for example, a forklift or the like. In this apparatus, a working oil at an amount corresponding to an operation amount of a steering wheel is supplied to a steering cylinder, and the steering cylinder is driven, whereby the steered tire wheel is steered in correspondence to the operation amount of the steering wheel. In this kind of industrial vehicle, there is a structure in which a knob is provided in the steering wheel so that the steering wheel can be operated by one hand while performing a loading operation by the other hand. There is a case where a driver sets a position of the steering wheel knob to a target for judging where the wheel angle of the steered tire wheel is. However, in the total hydraulic type steering apparatus, there is a problem that a deviation is caused in the positional relation between the position of the steering wheel knob and the wheel angle of the steered tire wheel, for the reason of a little deviation between the steering wheel operation amount and the supplied oil amount, an oil leakage or the like.
In order to solve the problem, a steering wheel angle compensating apparatus which compensates a deviation between the steering wheel angle and the wheel angle is disclosed, for example, in Japanese Examined Patent Publication No. Hei 3-30544 and Japanese Examined Patent Publication No. Hei 4-24270. That is, as shown in FIG. 21, a power steering apparatus 51 is provided with a controller 52, and the controller 52 inputs a steering wheel rotational signal xcex8abs from a steering wheel angle sensor 53, and inputs a cylinder stroke signal xe2x80x9csxe2x80x9d from a cylinder position sensor 54.
The controller 52 determines a target cylinder stroke from the steering wheel rotational signal xcex8abs. Further, when a deviation between the cylinder stroke determined from the cylinder stroke signal xe2x80x9csxe2x80x9d and a target cylinder stroke exceeds an allowable value, it opens an electromagnetic control valve 55. Accordingly, a part of working oil flows back to a tank 58 from one supply line of hydraulic lines 56 and 57 via another return line, a steering wheel 59 goes in a racing state, and a steering wheel position (a knob position) is compensated to a normal position in correspondence to the wheel angle of the steered tire wheel.
Further, as a steering apparatus in which the steering wheel and the steered tire wheel are not mechanically connected, a total electric type steering apparatus shown in FIG. 22, is disclosed in Japanese Unexamined Patent Publication No. Hei 7-206399. An order picking truck 61 is provided with a controller 62, and the controller 62 inputs a rotational angle of a steering wheel 63 from a potentiometer 64 and inputs a steering wheel (a wheel angle) of a steered tire wheel 65 from a potentiometer 66. Further, the controller 62 computes a deviation in a detection electric voltage between the potentiometers 64 and 66, and outputs a drive electric voltage corresponding to the deviation to a steering motor 67. Accordingly, the steered tire wheel 65 is steered so as to become a wheel angle corresponding to the operation angle of the steering wheel 63.
In this case, in the total hydraulic type steering apparatus, the steering wheel 59 and the steering cylinder 60 are connected via a hydraulic circuit. Accordingly, even when the working oil is flowed back via the electromagnetic control valve 55 during a period of executing the compensation of the steering wheel angle, a certain degree of holding force is secured in the steered tire wheel due to an existence of the working oil in the steering cylinder 60. That is, even when an external force is applied to the steered tire wheel, the steered tire wheel is not displaced until a force sufficient for pushing out the working oil within the steering cylinder 60 so as to drive the steering cylinder 60 is applied.
On the other hand, the total electric type steering apparatus is of a so-called steer-by-wire type in which the steering wheel 63 and the steered tire wheel 65 are not connected neither in a mechanical manner nor in a hydraulic circuit manner. Accordingly, since there is established a state in which a power is not transmitted to the steered tire wheel 65 in the case where the steering wheel 63 is stopped and the steering motor 67 is in a stop state, the holding force of the steered tire wheel by an operating mechanism including the steering wheel becomes comparatively weak. In particular, in the case of applying the steering wheel position compensating apparatus to the total electric type steering apparatus mentioned above, the holding force of the steered tire wheel 65 is lowered in the case of stopping driving the steering motor 67 for causing the racing of the steering wheel 68. For example, when the steered tire wheel steps on an obstacle (a stone or the like) on a traveling road surface, there has been a risk that the wheel angle of the steered tire wheel 65 deviates with respect to the steering wheel due to the external force.
In the case of employing the steering wheel position compensation, if the deviation exists between the steering wheel and the steered tire wheel, an output of the steering motor 67 is stopped during a period that the deviation exists, and the steering motor 67 is driven after the deviation does not exist. For example, during the straight traveling, there is executed an operation of fine operating the steering wheel 63 rightward or leftward so as to control a straight moving property. At this time, a direction of operating the steering wheel is switched little by little.
In this case, when the steering wheel is operated in a direction in which the deviation becomes small, the motor is stopped, and when the steering wheel is operated in a direction in which the deviation becomes large, the motor is driven. Accordingly, during a process of operating the steering wheel from a left turning point to a right turning point within the fine operation range, for example, within a narrow range of between 2xc2x0 and 10xc2x0 in one direction, the compensation is executed for canceling the deviation and the motor is stopped in a first half of the narrow range, and the compensation is inhibited for preventing the deviation from being made wide and the motor is driven in a second half of the narrow range. Accordingly, when the driver operates the steering wheel in one direction for the fine operation, a phenomenon that the motor output suddenly arises is easily generated in the second half.
In this case, there has been a problem that it is hard to secure a straight moving stability of the steering wheel operation, because the vehicle tends to be steered in a little serpentine manner even if the driver intends to generally fine operate the steering wheel for controlling the straight moving property. In particular, when turning a corner for right turn or left turn, the steering wheel is fine adjusted for getting right the straight moving property at a time of returning to the straight moving state from the curve traveling state, but a higher straight moving stability is required at a time of getting right an attitude of the vehicle. Accordingly, there has been required a countermeasure by which the positional relation between an actual position (the present rotational position) of the steering wheel and the wheel angle of the steered tire wheel is fitted, the output change of the steering motor 67 against the steering wheel operation before and after being switched from the compensation allowing state to the compensation inhibiting state is made as small as possible, and the straight moving stability of the steering wheel operation can be secured. This point is not limited to the total electric type steering apparatus, but is a problem in the total hydraulic type steering apparatus in the same manner.
The present invention has been achieved by taking the problems mentioned above into consideration, and a first object of the present invention is to provide a steering wheel position compensating apparatus in a total electric type steering apparatus which can secure a holding force of a steered tire wheel even during a period of executing a steering wheel position compensation, and a vehicle.
A second object is to make an output difference of driving means between before and after a positional relation between an actual position of the steering wheel and a wheel angle of the steered tire wheel fits so as to be switched from a compensating state to a compensation inhibiting state small, for example, to secure a straight moving stability of the steering wheel operation.
To achieve the foregoing and other objectives and in accordance with the purpose of the present invention, a steering apparatus of a vehicle provided with a steered tire wheel which is steered in correspondence to an operation of a steering wheel is provided. The apparatus includes first detecting means, second detecting means, electric type drive means, and compensating means. The first detecting means detects an actual position indicating a present rotational position of the steering wheel. The second detecting means detects a wheel angle of the steered tire wheel. The electric type drive means drives the steered tire wheel and outputs a power output for operating the steered tire wheel in correspondence to a steering wheel operation. The compensating means executes a first compensation for compensating an actual position of the steering wheel. The compensating means controls the power output of the drive means at a time when a deviation is detected between the actual position of the steering wheel detected by the first detecting means and a wheel angle of the steered tire wheel detected by the second detecting means, thereby reducing the deviation.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.